Such devices have become known as so-called compression and traction devices, especially from G. A. Ilisarov and U.S.S.R. patent No. 5387103338801/28-13 and from Italian patent No. 47890-A/82. These are splints consisting of rings and/or ring sections in which there are tension wires for bone fixation arranged crosswise in pairs or individually in each ring or ring-section level, whereby the various rings are connected to each other by means of rods, and the intervals of the ring levels are adjusted by rods of different lengths or by rods whose length can be varied telescopically. These bone fixation devices according to Ilisarov, which function by means of a cylindrical frame and tension wires, have proven to be superior to polygonal frame splints or to rod splints positioned para-axially to the bone. Just to mention the main advantages, in many situations, ring-wire splints can be fitted on an out-patient basis and under local anesthesia. They can be used to set bones three-dimensionally in a stereognostically clear manner, and secondary adjustment work can be done equally accurately with them. Without endangering the nutrition situation of the tissue and without the risk of weakening the stability, any wires can be subsequently attached, removed or replaced. Unlike the rigidly anchored rod and frame splints, the treatment with such ring-wire splints is designed as a prolonged, continuously progressing operation process. Failures that would have been ascribed to unsuccessful or improperly performed operations at a certain point in time are inconceivable here because of the process characteristic involving the constant possibility of progressive correction. Ilisarov's ring fixation techniques are largely subordinated to the biological healing process since, method-related, early stress of the limbs provides relevant information on the processes of callus formation and bone transformation, as they occur within the context of natural self-organization and autoregulation. After all, the flux of force is maintained as a function of the stress for such concentrically positioned fractures or osteotomies, whereupon nature, within the scope of self-organizational and autoregulatory consolidation, generates distinguishable building material in the fracture or osteotomy zone and arranges it stress-specifically, in a locally selective manner, in response to compression and tension. Since the ring splints, as an external stabilization frame, are stable with regard to jolting, bending and torsion, thanks to their cylindrical structure, and since flexible bone-penetrating wires serve as very stable anchoring bearings, it is possible to stimulate certain tissue-forming and reshaping processes within the scope of the physiological reaction spectrum, processes which are regulated by the adaptable flexibility of the wires; consequently, new bone formation can be controlled very accurately for the sake of therapeutic repair and regeneration.
In principle, the Ilisarov ring appliances can be fitted for most stereometric situations. However, many changes in shape and tension cannot be carried out with adequate precision and, in view of the frequency of the necessary correction steps, they cannot be carried out as simply and quickly as would be desirable. Moreover, the inevitably inconsistent manipulation of the original ring splints and the various replicas make it impossible to reliably assure the consistency necessary for the progressive healing procedure of this externally and dynamically affixed osteosynthesis therapy.
A ring splint with improved flexibility has been disclosed in West German patent DE-OS 3,439,795, which relates to a device to set bone segments and/or bone fragments, with which device the connection rods between the rings are connected to the rings in such a way that they can be pivoted within predefined but narrow limits in all directions and can be secured in any pivoted position, whereby the intervals between the adjacent rings in different levels can be adjusted independently of the selected pivot position of the rods; however, not the entire circumference of the rings is available for affixing the connection rods, but rather, the attachment is limited only to certain places along the circumference of the rings, which are provided with a number of bore-holes. This device allows a certain dislocation-free neutralization of the forces being exerted, but nevertheless, in spite of its improved three-dimensional adaptation possibilities, it is not able to sufficiently fulfill the prerequisites of an operation technique aimed at natural causal histogenesis. First of all, the rings, as in the Russian device, are transversally positioned surface sections with a cumbersome, large outer circumference. Second, the connection rods between two rings can only be affixed at certain predefined places along the rings, as a result of which it is not possible to slide the ends of the connection rods along the rings completely at will. Third, the spatial wire control for the tension wires of the known appliance is insufficient because the tension wires can be placed under tension practically only in the direction of the diameter, and an off-center wire position is associated with a risky bending of the wires. Fourth, in order to tighten and retighten the wires, special wire stretchers are needed, which have to be made specially for this stretching procedure. Fifth, with the known ring splint, it is not possible to use the connection rods as torsion-free, axially supported anchoring sites for the tension wires to be stretched between the ring levels. Sixth, there is only the possibility for frictionally engaged and not linearly engaged clamping attachment in the pivot bearings of the rods.